The present invention relates to the field of wireless communications. More specifically, the present invention relates to detecting codes in a communication signal in order to activate the receiver to process the signal.
Spread spectrum TDD systems carry multiple communications over the same spectrum. The multiple signals are distinguished by their respective chip code sequences (codes). Referring to FIG. 1, TDD systems use repeating transmission time intervals (TTIs), which are divided into frames 34, further divided into a number of timeslots 371–37n,, such as fifteen timeslots. In such systems, a communication is sent in a selected timeslot out of the plurality of timeslots 371–37n using selected codes. Accordingly, one frame 34 is capable of carrying multiple communications distinguished by both timeslot and code. The combination of a single code in a single timeslot is referred to as a physical channel. A coded composite transport channel (CCTrCh) is mapped into a collection of physical channels, which comprise the combined units of data, known as resource units (RUs), for transmission over the radio interface to and from the user equipment (UE) or base station. Based on the bandwidth required to support such a communication, one or multiple CCTrChs are assigned to that communication.
The allocated set of physical channels for each CCTrCh holds the maximum number of RUs that would need to be transmitted during a TTI. The actual number of physical channels that are transmitted during a TTI are signaled to the receiver via the Transport Format Combination Index (TFCI). During normal operation, the first timeslot allocated to a CCTrCh will contain the required physical channels to transmit the RUs and the TFCI. After the receiver demodulates and decodes the TFCI it would know how many RUs are transmitted in a TTI, including those in the first timeslot. The TFCI conveys information about the number of RUs.
FIG. 1 also illustrates a single CCTrCh in a TTI. Frames 1, 2, 9 and 10 show normal CCTrCh transmission, wherein each row of the CCTrCh is a physical channel comprising the RUs and one row in each CCTrCh contains the TFCI. Frames 3–8 represent frames in which no data is being transmitted in the CCTrCh, indicating that the CCTrCh is in the discontinuous transmission state (DTX). Although only one CCTrCh is illustrated in FIG. 1, in general there can be multiple CCTrChs in each slot, directed towards one or more receivers, that can be independently switched in and out of DTX.
DTX can be classified into two categories: 1) partial DTX; and 2) full DTX. During partial DTX, a CCTrCh is active but less than the maximum number of RUs are filled with data and some physical channels are not transmitted. The first timeslot allocated to the CCTrCh will contain at least one physical channel to transmit one RU and the TFCI word, where the TFCI word signals that less than the maximum number of physical channels allocated for the transmission, but greater than zero (0), have been transmitted.
During full DTX, no data is provided to a CCTrCh and therefore, there are no RUs at all to transmit. Special bursts are periodically transmitted during full DTX and identified by a zero (0) valued TFCI in the first physical channel of the first timeslot allocated to the CCTrCh. The first special burst received in a CCTrCh after a normal CCTrCh transmission or a CCTrCh in the partial DTX state indicates the start of full DTX. Subsequent special bursts are transmitted every Special Burst Scheduling Parameter (SBSP) frames, wherein the SBSP is a predetermined interval. Frames 3 and 7 illustrate the CCTrCh comprising this special burst. Frames 4–6 and 8 illustrate frames between special bursts for a CCTrCh in full DTX.
As shown in Frame 9 of FIG. 1, transmission of one or more RUs can resume at any time, not just at the anticipated arrival time of a special burst. Since DTX can end at any time within a TTI, the receiver must process the CCTrCh in each frame, even those frames comprising the CCTrCh with no data transmitted, as illustrated by Frames 4–6 and 8. This requires that the receiver operate at high power in order to process the CCTrCh for each frame, regardless of its state.
Receivers are able to utilize the receipt of subsequent special bursts to indicate that the CCTrCh is still in the full DTX state. Detection of the special burst, though, does not provide any information as to whether the CCTrCh will be in the partial DTX state or normal transmission state during the next frame.
Support for DTX has implications to several receiver functions, notably code detection. If no codes are sent in the particular CCTrCh in one of its frames, the code detector may declare that multiple codes are present, resulting in a Multi-User Detector (MUD) executing and including codes that were not transmitted, reducing the performance of other CCTrChs that are also processed with the MUD. Reliable detection of full DTX will prevent the declaring of the presence of codes when a CCTrCh is inactive. Also, full DTX detection can result in reduced power dissipation that can be realized by processing only those codes that have been transmitted and not processing empty timeslots.
Accordingly, there exists a need for an improved receiver.